Vacuum insulated converter for extending the life span of electronic components

ABSTRACT

A system for extending the life span of electronic components in a high temperature well. A thermal electric cooler is located in a position thermally communicating with the electronic component in the well. The thermal electric cooler lowers the temperature of the electronic component to a temperature that retards the deterioration of the electronic component, and is particularly useful in well completion tools requiring an extended life. A vacuum is maintained about the thermal electric cooler or the electronic components to reduce convection energy losses.

This patent application is a continuation-in-part application based onU.S. Ser. No. 08/304,698 filed Sep. 12, 1994, entitled "Downhole Systemfor Extending the Life Span of Electronic Components" now U.S. Pat. No.5,547,028.

BACKGROUND OF THE INVENTION

The present invention relates to the use of electronic components in awell. More particularly, the present invention relates to a system forextending the life span of downhole electronic components in a well.

The development of hydrocarbon producing wells requires the installationof well completion equipment to monitor and control the flow of fluids.The characteristics of the well are monitored by the completionequipment and are transmitted to the surface. The transmitted data isanalyzed by a reservoir management system, and completion equipment suchas valves, sliding sleeves, packers, and other completion tools aremodified to control the well.

Electronic systems have been incorporated into well completionequipment. However, these downhole electronic systems do not adequatelyperform for the producing life of the well, which can typically last forten or more years. When the electronic components in the equipment fail,reservoir management data is interrupted until the equipment isrepaired. The repair of such equipment interrupts the operation of thewell and increases production cost.

This limitation in the life span of downhole electronic systems is atleast partially attributable to elevated temperatures found in certainwells. Downhole well temperatures can exceed 150 degrees Celcius, andthese temperatures affect the operation of integrated circuitsconstructed with electronic components.

Efforts have been made to overcome the limitations of electronic devicesat elevated temperatures by using fiber optics. One example is a downhole pressure guage system which does not include downhole electronics.The guage senses pressure through a response created by the change inrefractive index of a material in response to pressure variations. Thisresponse is measured at the surface by monitoring the changes of anoptical signal transmitted from the surface to the downhole guage andback to the surface through a fiber optic cable. While optical systemsmay be beneficial with certain guage types, optical systems are limitedbecause many well bore characteristics cannot provide a direct opticalresponse. Optical systems are also limited because sufficient powercannot be transmitted through such systems to manipulate downholemechanical tools for controlling the flow of fluids. Consequently,optical systems cannot provide equivalent functionality to electronicsolutions for the downhole processing of information or the regulationof power.

Although systems for extending the life span of electronic components inwell completion tools have not been developed, well logging tools haveused insulating flasks to shield electronic components from elevatedwell temperatures. For example, Dewar flasks maintain the electroniccomponents within certain temperature ranges to prevent unstable circuitoperation. Although Dewar flasks temporarily insulate the electroniccomponents, the temperature inside the Dewar flask eventually equalizeswith the well temperature.

Various concepts to improve the insulating performance of a Dewar flaskhave been proposed. For example, U.S. Pat. No. 3,265,893 to Rabson etal. (1966) described a well logging tool having a thermally conductiveheat sink for stabilizing the temperature in the logging tool for up totwenty hours. U.S. Pat. No. 4,671,349 to Wolk (1987) described a heattransfer wick for cooling the components of a well logging instrumentfor up to six hours during the interval of greatest heat exposure.

Another concept for improving the performance of a Dewar flask wasdescribed in U.S. Pat. No. 3,488,970 to Hallenburg (1970). Electriccomponents were insulated from the well temperature by a Dewar flask,and a pump transported water through a conduit to transfer internallygenerated heat from the electic components to a water reservoirpositioned beneath the Dewar flask. Upper and lower temperature switchescontrolled the pump operation to heat and cool the Dewar flask within aselected temperature range. A thermoelectric cooling module transferredheat between the water reservoir and the borehole through the loggingtool housing. The water reservoir was located at a position away fromDewar flask so that heat transferred by the thermoelectric coolingmodule was discharged at a position distant from the Dewar flask.

Another concept was described in DOE Technical Note DOE/TIC/EG-85/054 byBennett entitled Improved Thermal Protection Apparatus for Electronics.This proposal used methanol carrying tubes to transfer heat from theelectronics to a heat sink of ice so that the electronic componentswould be protected for up to ten hours at 235 degrees C. Bennettdescribed another concept in a Journal of Energy Resources Technologyarticle entitled Analytical Approach to Selecting and Designing aMinature Downhole Refrigerator (December 1992).

None of these concepts describe a system for extending the life span ofelectronic components in well completion tools. Consequently, a needexists for an apparatus and method which extends the life span ofelectronic components exposed to elevated temperatures during theproduction life of a well.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for extending thelife span of electronic components in a well. The apparatus of theinvention is engaged with an electric power source and includes aconnecter for engagement with the power source. A converter located witha housing interior space transforms power into thermal energy to createa converter cold surface for cooling the electronic component and tocreate a converter hot surface for dissipating thermal energy away fromthe converter. A vacuum is maintained within the interior space toreduce convection energy losses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a Bathtub curve.

FIG. 2 illustrates the performance of electronic components at differenttemperatures.

FIG. 3 illustrates the position of one embodiment of the invention in atubular well tool.

FIG. 4 illustrates an enlarged sectional view of one embodiment of theinvention.

FIG. 5 illustrates a schematic view of the invention showing two thermalelectric coolers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a novel apparatus and method forextending the life span of electronic components located in wells. Theinvention is particularly useful in well control and monitoring systemsthat remain downhole for extended periods of time.

The life span of an electronic component is critical to the actual useof the electronic component in a well, The "life span" of an electroniccomponent differs from the "reliability" of the electronic component andmore accurately defines the utility of a downhole completion system.

Modern electronic components such as Hi-Rel type components have highreliability. Although such components are extremely reliable, the actualuse of a manufactured population of electronic components is hampered byseveral factors. The statistical analysis for the reliability of anelectronic component population can be represented by a "Bathtub Curve"as shown in FIG. 1. The horizontal axis represents time, and thevertical axis represents the failure rate of the electronic component.As used throughout this application, the term "reliability" means theprobability that an item will perform its intended function withoutfailure for a specified time period under specified conditions. TheBathtub curve in FIG. 1 also shows that the reliability of a componentpopulation changes over time.

FIG. 1 demonstrates that the reliability of a sample population ofmanufactured components is initially poor. This early period, shown as aperiod of decreasing failure probability, is known as a period of"infant mortality". Failure due to infant mortality typically occursbecause of manufacturing or material flaws. Over time, the reliabilityof the components approaches a substantially constant level, shown asthe middle part of the curve in FIG. 1. This period is termed the periodof "useful life" or "life span", and substantially indicates the periodof reliable operation.

After the life span period has concluded, "wear out" failures occur. Thewear out period of time is characterized by a substantial increase infailure rate plotted against time.

FIG. 2 shows that the "life span" of an electronic component decreasesexponentially as temperature increases. This principle is mathematicallystated by the Arrhenius equation, and broadly defines the performance ofsemiconductor devices over time. Because of this relationship, the lifespan of an electronic component is approximately halved for every tendegrees increase in temperature. Studies have shown that the life spanof an integrated circuit population was 117.8 years at 80 degreesCentigrade and was reduced to one year at 140 degrees Centigrade.

The present invention enhances the utility of electronic components indownhole wells by extending the life span of the electronic componentsin elevated temperature environments. Referring to FIG. 3, converter 10is illustrated as a thermal electric cooler ("TEC") attached to welltool 12. Connecter 14 is attached to TEC 10 and is further attached toelectrified wire 16. To shield TEC 10 from physical damage, TEC 10 ispositioned in recess 18 located in tool 12. Electronic component 20 islocated proximate to TEC 10 as more fully described below, and connecter14 extends through aperture 22 of tool 12. Seal 24 prevents reservoirfluids 26 from intruding into recess 18, and reservoir fluids 26 enterthe well string at a location (not shown) below tool 12 and travelupwardly through bore 28 through tool 12.

Is the usual operation shown in FIG. 3, TEC 10 has cold surface 30 andhot surface 32. Thermal conductor 34 is positioned between cold surface30 and electronic component 20 and thermal conductor 36 is positionedbetween hot surface 32 and tool 12. Thermal grease 38 is positionedbetween all thermal contact surfaces as illustrated, and enhances thethermal conductivity between such contact surfaces by filling small gapsand irregularities between such surfaces. Cover 40 further protects TEC10 from impacts and from the intrusion of reservoir fluids 26, andO-ring seal 42 seals the joint between cover 40 and tool 12.

Electronic component 20 is described herein as any electronic or solidstate component. Electronic component 20 can comprise any materialhaving a life span less than the design requirements of a well or lessthan mechanical tool components in a downhole well tool. Alternatively,electronic component 20 can comprise a material that deteriorates whenexposed to well temperatures higher than ambient temperature at thesurface. As previously noted, the deterioration can be partial orcomplete and can result in loss of performance or complete failure ofthe component. Electronic components 10 are typically combined in anintegrated circuit to perform a desired task or function, and suchelectronic components can comprise circuit chips, transistors,resistors, and other components known in the art.

Although the thermal converter is illustrated as TEC 10, thermalconverter could comprise any tool or equipment that cools electroniccomponent 20. TEC 10 represents one useful form of converter to performthis function. As known in the art, TEC 10 creates cold surface 30 andhot surface 32 when charged with an electric current. TEC 10 comprises aset of alternately negatively and positively doped semiconductor regionselectrically coupled in series and sandwiched between two electricallyinsulative and thermally conductive layers such as ceramic substrates.As current flows through the semiconductors, heat is conducted from onedielectric layer to the other dielectric layer to create cold and hotsurfaces respectively. Additional temperature differential between coldsurface 30 and hot surface 32 can be achieved by combining one or moreTECs in series wherein first cold surface 30 contacts the hot surface ofthe second TEC.

As shown in FIG. 3, cold surface 30 is positioned proximate toelectronic component 20 so that the cooling effect of cold surface 30withdraws thermal energy from electronic component. Hot surface 32 isshown in contact with tool 12 so that tool 12 acts as a heat sink todissipate thermal energy away from TEC 10. If fluid 26 has a temperatureless than tool 12 and is moving through bore 28 as shown in FIG. 1,fluid 26 can also facilitate the dissipation of heat from TEC 10.

It will be appreciated that hot surface 32 does not need to be connectedto tool 12, and that hot surface 32 can dissipate heat in other ways toremove thermal energy from TEC 10. For example, hot surface 32 could bein contact with fluid 26 within bore 28 or could contact fluid 26 in theannulus between tool 12 and the wellbore. These various embodiments ofthe invention relate to the thermal efficiency in removing heat awayfrom TEC 10, and further contemplate the use of alternative heat sinkdesigns known in the art.

Referring to FIG. 4, an alternative embodiment of the invention isillustrated. TEC 10 is positioned in recess 44 of tubular flowline 46,and thermal conductor 48 is located between TEC 10 and flowline 46.Printed Circuit Board Assembly ("PCBA") 50 is generally located inrecess 44 and is thermally insulated from reservoir fluids 26 withinsulated cover 52. Insulated cover 52 increases the cooling efficiencyof TEC 10 by reducing the thermal losses caused by convection of air andother elements in contact with PCBA 50.

In another embodiment of the invention, interior space 53 is defined asthe volume between cover 52 and flowline 46. PCBA 50 and TEC 10 arepositioned within space 53, and a vacuum is created within space 53. Theattachment between cover 52 and flowline 46 is sufficiently sealed withtechniques known in the art to maintain such vacuum. The presence of avacuum within space 53 substantially reduces convection energy losses asTEC 10 is operated. Convection energy losses exceed radiation losses andreduce the operating efficiency of TEC 10 in cooling electroniccomponents 54. By substantially eliminating convection losses throughthe maintenance of a vacuum within space 53, the operating efficiency ofTEC 10 increases, and TEC 10 requires less power to cool electroniccomponents 54. In one embodiment of the invention, electronic components54 can be positioned within space 53 to reduce convection currentscirculating around electronic components 54.

As shown in FIG. 4, PCBA 50 includes electronic components 54 of varyingconfigurations and heights (as measured from base 56) to form anirregular profile. Thermal conductor 58 is positioned between coldsurface 60 of TEC 10 and includes shaped surface 62 generally configuredto mirror the irregular profile of electronic components 54. In thismanner, space between shaped surface 62 and electronic components 54 isminimized to improve thermal heat transfer therebetween. In a preferredembodiment of the invention, shaped surface 62 contacts each electroniccomponent 54 to provide thermal conductivity therebetween. This featurepermits conductive thermal transfer of energy between shaped surface 62and electronic components 54 forming an irregularly shaped profile.

In another embodiment of the invention, thermal conductor 58 cancomprise a liquid material which solidifies around electronic components54 to form a conductivity path having an irregular shape. Alternatively,thermal conductor 58 can comprise any material which forms a conductivepath between the cold surface of a TEC and one or more components of aPCBA.

As previously described, thermal grease 38 or similar medium can furtherenhance thermal conductivity. This embodiment of the inventionsignificantly enhances the efficient transfer of thermal energy fromPCBA 50 to flowline 46 by using conductive thermal transfer instead ofconvective thermal transfer. Moreover, this embodiment is significantlymore efficient than cooling systems that rely on the circulation of acooling medium to a remote heat sink.

FIG. 5 illustrates an alternative embodiment of the invention whereinmultiple TEC's are combined in a cooling system. TEC 64 and TEC 66 arelocated proximate to PCBAs 68 and 70 respectively. Electrified conductoror wire 72 is connected to TEC 64 and TEC 66 and extends to the wellsurface. Controller 74 is located at the well surface and communicateswith TEC 64 and TEC 66. Controller 74 also communicates with temperaturegauge 76 and temperature gauge 78 which are respectively positioned todetect the temperatures of PCBAs 68 and 70. Although the signalcommunication between controller 74 and TEC's 64 and 66 and temperaturegauges 76 and 78 is illustrated as being accomplished through wire 72which can comprise an instrument wire ("I wire") in one embodiment, itwill be appreciated that such communication can be accomplished throughdifferent techniques known in the art. In one embodiment of theinvention, either wire 72 or other type of conductor can simultaneouslytransmit signals and to transmit power for operation of TECs and otherdownhole equipment.

The conductive capability of wire 72 is limited by the resistance perlength of wire. The voltage drop across the resistance of the wireincreases with the square of the current. The present invention managesthis limitation by controlling the amount of power supplied to one ormore thermal converters or other power device. As shown in FIG. 5,voltage is measured at end of wire 72 by downhole controllers 82.Downhole controllers 82 are in communication with controller 74 at thesurface and can communicate voltage value. Downhole controllers 82 canalso modulate power to TECs 64 and 66. In one embodiment of theinvention, downhole controllers 82 increase power to TECs 64 and 66until voltage at end of wire 72 decreases below a critical level.

In one form of the embodiment shown in FIG. 5, two or more downholecontrollers 82 can be engaged with TECs 64 and 66 at different parts ofthe well. Because each of the downhole controllers 82 may requiredifferent thermal energy levels to sustain PCBAs 68 and 70 at selectedtemperatures, controller 74 can modulate the power to each downholecontroller 82.

Temperature gauges 76 and 78 monitor the temperature of PCBAs 68 and 70and communicate such information to controller 74. This temperatureinformation is processed and a control signal is sent by controller 74to TECs 64 and 66. If TEC 66 is connected to wire 72 at a location moredistant from controller 74 than TEC 64, and if the temperature desiredfor PCBA 68 and PCBA 70 is the same, TEC 66 will require a higherpercentage of the total power transmitted through wire 72 than will TEC64.

In another embodiment, controller 74 can iteratively measure thetemperature of each PCBA and selectively modify the power supplied toeach TEC until the desired condition is reached. Under this embodiment,controller 74 can actively search for the optimal cooling power whilelimiting the total amount of power transmitted through wire 72. In oneconfiguration of this embodiment, each PCBA would measure the voltagepotential at the respective TEC and then transmit such data tocontroller 74. Each PCBA would also modulate the amount of power intothe respective TEC. Controller 74 would supply the maximun permissiblevoltage to wire 72, and would request each PCBA to report the voltagedata experienced. Controller 74 would then compare the respectivevoltages. If the voltage is above the drop out voltage, controller 74would then increase the power to the TECs by a selected factor and wouldrepeat the process described above. By repeating this process, themaximum amount of power that can be managed by the entire system can bedetermined and tested.

In a system having two or more TECs or other thermal converters, eachTEC will likely experience a different ambient temperature within thewellbore. Each PCBA can have the capability described above in additionto other capabilities. For example, each PCBA could measure the voltageof the hot and cold surfaces of each TEC, could transmit such data tocontroller 74, and could be capable of modulating the power to therespective TEC. Controller 74 could read the cold side temperature andthe voltage at each TEC. If the PCBA drop out voltage is known,controller 74 could instruct the PCBA with the highest TEC temperatureto increase the power to the TEC by a selected amount until thetemperature is below the temperature of the other TEC. Conversely, theprocess could be repeated for the new TEC having the highesttemperature. In this fashion, the overall power distributed through wire72 substantially remains constant at the maximum level while thetemperature of each TEC is reduced to the greatest extent possible.

In another embodiment of the invention, the selective operation of eachPCBA and TEC could be controlled independently of temperaturerequirements. For example, it may be desirable to selectively activateor interrupt the supply of power to a selected TEC, and controller 74could be programmed to accomplish this task.

The present invention extends the life span of selected electroniccomponents by lowering the temperature of such components and bylowering the junction temperature between such components and otherelements in the system. By providing an efficient thermal conductivitypath, the invention efficiently cools the electronic components with aminimal amount of power.

The invention further permits the efficient allocation of a limitedpower source to a single thermal converter or to a combination ofthermal converters. This feature balances the cooling operation of theentire tool string while preventing disruptions to the power source andtransmission system. In different embodiments of this feature, thetemperatures of selected tools or electronic components in tools can bemonitored and adjusted to meet desired operational parameters.Consequently, the available power can be transmitted to control theefficient operation of a single component or of several components inthe well string.

Although the present invention is particularly, useful in hightemperature wells, the invention concepts are useful in applicationsrequiring extended tool service over a long production life, or inapplications where the repair costs of replacing failed componentssubstantially exceed the preventative maintenence cost of the system.

Although the invention has been described in terms of certain preferredembodiments and procedures, it will be apparent to those of ordinaryskill in the art that various modifications and improvements can be madeto the inventive concepts herein without departing from the scope of theinvention. The embodiments described herein are merely illustrative ofthe inventive concepts and should not be interpreted as limiting thescope of the invention.

What is claimed is:
 1. An apparatus engaged with an electric powersource for extending the life span of an electronic component in a well,comprising:a housing defining an interior space within the well, whereina vacuum is maintained within said interior space; a connecter forengagement with the electric power source; and a converter locatedwithin said housing interior space, wherein said converter is engagedwith said connecter for transforming power from the electric powersource into thermal energy to create a cold surface for cooling theelectronic components, and to create a hot surface for dissipatingthermal energy away from said converter.
 2. An apparatus as recited inclaim 1, wherein the electronic component is positioned within saidhousing interior space.